Method and device for controlling generator-side terminal voltage of converter, and controller of converter

ABSTRACT

The present application provides a method and device for controlling a generator-side terminal voltage of a converter, and a controller of the converter. The method includes: determining a target value upper limit of the generator-side terminal voltage based on a current voltage value of a direct-current (DC) bus of the converter, wherein the generator-side terminal voltage is a terminal voltage of a generator whose output terminal is connected to the converter; determining a target value of the generator-side terminal voltage that is able to minimize a generator-side current at present, and using the determined target value of the generator-side terminal voltage as an optimal target value of the generator-side terminal voltage, wherein the generator-side current is an output current of the generator; setting the target value of the generator-side terminal voltage based on the determined target value upper limit of the generator-side terminal voltage and the optimal target value.

TECHNICAL FIELD

The present application generally relates to a technical field ofconverters, and in particular, to a method and device for controlling agenerator-side terminal voltage of a converter, and a controller of theconverter.

BACKGROUND

FIG. 1 illustrates a control method of a permanent-magnet direct-drivewind power converter to a terminal voltage of a generator. In FIG. 1 ,Us_ref is a control target value of a field weakening voltage, which isgenerally a constant value; Us_meas_flt is a feedback value of the fieldweakening voltage (which is generally an estimated value based on theactual operation); Iq_Ref is an reactive current reference valueobtained by PI adjustment of a tracking deviation of the field weakeningvoltage; Iqref_Max and Iqref_Min are output limit values of a PIadjuster. Taking Iq_Ref as a reference input of a current inner loop,the converter tracks the reactive current reference value and outputsthe reactive current, and the reactive current acts on the generator toadjust the field weakening voltage of the generator.

In the prior art, because that the control target value of the fieldweakening voltage is constant, there will be a problem of lowutilization of a direct-current (DC) voltage in some working conditions,a problem of overmodulation in some working conditions, and a problem oflow efficiency of the electric transmission chain.

SUMMARY

The exemplary embodiments of the present application provide a methodand device for controlling a generator-side terminal voltage of aconverter, and a controller of the converter, which can solve theproblems of low utilization rate of the DC voltage and overmodulationexisting in the prior art.

According to an exemplary embodiment of the present application, amethod for controlling a generator-side terminal voltage of a converteris provided. The method includes: determining a target value upper limitof the generator-side terminal voltage based on a current voltage valueof a direct-current (DC) bus of the converter, wherein thegenerator-side terminal voltage is a terminal voltage of a generatorwhose output terminal is connected to the converter; determining atarget value of the generator-side terminal voltage that is able tominimize a generator-side current at present, and using the determinedtarget value of the generator-side terminal voltage as an optimal targetvalue of the generator-side terminal voltage, wherein the generator-sidecurrent is an output current of the generator; setting the target valueof the generator-side terminal voltage based on the determined targetvalue upper limit of the generator-side terminal voltage and the optimaltarget value of the generator-side terminal voltage.

According to another exemplary embodiment of the present application, adevice for controlling a generator-side terminal voltage of a converteris provided. The device includes: a target value upper limitdetermination unit configured to determine a target value upper limit ofthe generator-side terminal voltage based on a current voltage value ofa direct-current (DC) bus of the converter, wherein the generator-sideterminal voltage is a terminal voltage of a generator whose outputterminal is connected to the converter; an optimal target valuedetermination unit configured to determine a target value of thegenerator-side terminal voltage that is able to minimize agenerator-side current at present, and using the determined target valueof the generator-side terminal voltage as an optimal target value of thegenerator-side terminal voltage, wherein the generator-side current isan output current of the generator; a target value setting unitconfigured to set the target value of the generator-side terminalvoltage based on the determined target value upper limit of thegenerator-side terminal voltage and the optimal target value of thegenerator-side terminal voltage.

According to another exemplary embodiment of the present application, acontroller of a converter is provided. The controller includes: aprocessor; a memory having computer programs stored thereon, wherein thecomputer programs, when executed by the processor, implement the methodfor controlling the generator-side terminal voltage of the converterdescribed above.

According to another exemplary embodiment of the present application, acomputer-readable storage medium having computer programs stored thereonis provided. The computer programs, when executed by a processor,implement the method for controlling the generator-side terminal voltageof the converter described above.

According to the method and device for controlling a generator-sideterminal voltage of the converter, and the controller of the converterin the exemplary embodiments of the present application, the controltarget value of the generator-side terminal voltage is dynamically setbased on the current voltage of the DC bus and the current operatingstate of the generator. Therefore, the utilization rate of the DCvoltage can be improved, the efficiency of the generator and theelectric transmission chain can be improved, and the problem ofovermodulation can be avoided, thereby improving the control stability.

Additional aspects and/or advantages of the general concept of thepresent application will be set forth in part in the followingdescription, and other parts will be apparent from the description, ormay be learned by practice of the general concept of the presentapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the exemplary embodiments ofthe present application will become more apparent from the followingdescription in conjunction with the accompanying drawings thatexemplarily illustrate the embodiments, in which:

FIG. 1 illustrates an example of obtaining a reactive current referenceby an existing converter;

FIG. 2 illustrates a flowchart of a method for controlling agenerator-side terminal voltage of a converter according to an exemplaryembodiment of the present application;

FIG. 3 illustrates a flowchart of a method for determining an optimaltarget value of a generator-side terminal voltage according to anexemplary embodiment of the present application;

FIG. 4 illustrates a structural block diagram of a controller of aconverter according to an exemplary embodiment of the presentapplication.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments of the presentapplication, and the examples of the embodiments are illustrated in theaccompanying drawings, wherein like reference numerals refer to likecomponents. The embodiments will be described below by referring to thefigures, so as to explain the present application.

The converter involved in the exemplary embodiments of the presentapplication includes a generator-side rectifier unit and a grid-sideinverter unit, and the output terminal of the generator is connected tothe power grid via the generator-side rectifier unit and the grid-sideinverter unit in sequence. For example, the converter may be a windpower converter, and accordingly, the generator may be a generator of awind turbine set.

FIG. 2 illustrates a flowchart of a method for controlling agenerator-side terminal voltage of a converter according to an exemplaryembodiment of the present application.

Referring to FIG. 2 , in step S10, a target value upper limit of thegenerator-side terminal voltage is determined based on a current voltagevalue of a DC bus of the converter. Therefore, the target value upperlimit of the generator-side terminal voltage may be associated with thevoltage of the DC bus in real time, and the target value upper limit ofthe generator-side terminal voltage can be dynamically changed with thechange of the voltage of the DC bus.

Here, the generator-side terminal voltage is a terminal voltage of agenerator whose output terminal is connected to the converter (i.e., theoutput terminal voltage of the generator). As an example, thegenerator-side terminal voltage may be a generator-side phase voltage ora generator-side line voltage.

Here, the target value of the generator-side terminal voltage is acontrol reference value of the generator-side terminal voltage, that is,a control target value of a field weakening voltage of the generator.

As an example, on the basis of the current voltage value of the DC busof the converter, the target value upper limit of the generator-sideterminal voltage may be determined further based on at least one of apreset maximum availability of a voltage of the DC bus, a voltage losscorresponding to a dead time of an IGBT module in a generator-siderectifier unit of the converter, and an on-state voltage drop of theIGBT module in the generator-side rectifier unit of the converter.

As an example, under a condition that the generator-side terminalvoltage is the generator-side line voltage, and considering that thecommonly used modulation technology of the converter is a space vectormodulation (SVPWM) method, the maximum availability of the DC voltage is1.1547 when this modulation method is adopted. The maximum line voltagevalue that can be modulated theoretically is shown in equation (1):

U _(linevoltage_max) =U _(dc)/√{square root over (2)}  (1)

Wherein U_(linevoltage_max) is the maximum value of the generator-sideline voltage that can be modulated theoretically, and U_(dc) is thevoltage value of the DC bus.

It can be seen from equation (1) that for the terminal voltage of thegenerator, the voltage of the DC bus limits its upper limit value.Therefore, under a condition that the DC voltage changes greatly, thecorresponding upper limit value of the terminal voltage of the generatoralso changes. That is, if the voltage of the DC bus is greatlyincreased, the maximum voltage that can be output by the converter willalso increase (at this time, using a fixed target value of the terminalvoltage of the generator may result in low utilization of the DCvoltage). If the voltage of the DC bus is greatly reduced, the maximumvoltage that can be output by the converter will also decrease (at thistime, using a fixed target value of the terminal voltage of thegenerator may result in overmodulation). Therefore, using a fixed targetvalue of the terminal voltage of the generator cannot adapt to thechange of the DC voltage, which brings the above problems. Thus, thepresent application proposes to determine the target value upper limitof the generator-side terminal voltage based on the current voltagevalue of the DC bus of the converter.

As an example, considering the influence of the tube voltage drop of thegenerator-side rectifier unit and the dead zone on the utilization ofthe DC voltage, the target value upper limit of the generator-sideterminal voltage may be calculated by equation (2) or equation (3):

$\begin{matrix}{U_{{ref\_ max}{\_ limit}} = {\frac{U_{dc\_ meas}}{\sqrt{2}} - U_{dead\_ time} - {VCE}_{sat}}} & (2)\end{matrix}$ $\begin{matrix}{U_{{ref\_ max}{\_ limit}} = {\frac{U_{dc\_ meas}}{\sqrt{2}} - U_{lost}}} & (3)\end{matrix}$

Wherein U_(ref_max_limit) is the target value upper limit of thegenerator-side terminal voltage, U_(do_meas) is the real-time voltagevalue of the DC bus of the converter, U_(dead_time) is the voltage losscorresponding to the dead time of the IGBT module in the generator-siderectifier unit (which can be calculated according to the dead time),VCE_(sat) is the on-state voltage drop of the IGBT module (which can beobtained from the datasheet of the IGBT), U_(lost) is the comprehensivevoltage drop obtained based on the equivalent voltage drop in the deadzone of the IGBT and the tube voltage of the IGBT.

In addition, as another example, under a condition that thegenerator-side terminal voltage is the generator-side phase voltage, thetarget value upper limit of the generator-side terminal voltage can becalculated by equation (4):

$\begin{matrix}{U_{{ref\_ max}{\_ limit}} = {\frac{U_{dc\_ meas}}{\sqrt{3}} - U_{dead\_ time} - {VCE}_{sat}}} & (4)\end{matrix}$

In step S20, a target value of the generator-side terminal voltage thatis able to minimize a generator-side current at present is determined,and the determined target value of the generator-side terminal voltageis used as an optimal target value of the generator-side terminalvoltage. In other words, under the current operating state of thegenerator, if the target value of the generator-side terminal voltage isset to the optimal target value of the generator-side terminal voltage,the generator-side current can be minimized; and the optimal targetvalue of the generator-side terminal voltage can be dynamically changedwith the change of the operating state of the generator.

Here, the generator-side current is an output current of the generator.

The present application considers that, for example, for apermanent-magnet direct-drive generator, as the operating parameter suchas the operating environment temperature changes, the operating voltageand current curves will change differently. For example, the currentvalues under the same terminal voltage of the generator will bedifferent. If a constant target value of the terminal voltage of thegenerator is used, it cannot adapt to the change of the operating state,and the goal of minimizing the current of the generator cannot beachieved, thereby reducing the efficiency of the system. Therefore, thepresent application takes the minimized generator-side current as thegoal, and searches for the optimal target value of the terminal voltageof the generator, so as to improve the efficiency of the electricaltransmission chain of the generator. Therefore, the calorific value ofthe generator and the converter during operation can be reduced, theworking load of the cooling devices of the generator and the convertercan be reduced, and the working life of the cooling devices can beincreased.

As an example, it can be determined whether the current generator-sideterminal voltage belongs to a preset optimal search interval [U_(min),U_(max)]; and under a condition that it is determined that the currentgenerator-side terminal voltage belongs to the optimal search interval,the target value of the generator-side terminal voltage may be set todifferent values in the optimal search interval in sequence, so as tosearch for the target value of the generator-side terminal voltage thatis able to minimize the generator-side current at present. Specifically,based on the generator-side current corresponding to the target value ofthe generator-side terminal voltage being set to different values in theoptimal search interval in sequence, a value can be searched out fromthe optimal search interval. If the target value of the generator-sideterminal voltage is set to this value, compared with other values in theoptimal search interval, the generator-side current can be minimized.

Here, U_(min) and U_(max) can be determined according to the parametersof the generator. Under a condition that the generator-side terminalvoltage belongs to the optimal search interval, the generator-sideterminal voltage is in a controllable state (that is, the generator-sideterminal voltage can be effectively controlled).

It should be understood that under a condition that the currentgenerator-side terminal voltage does not belong to the optimal searchinterval, the method for controlling the generator-side terminal voltageof the converter according to the exemplary embodiments of the presentapplication may be stopped, and the method may be executed again untilthe next execution cycle comes.

As an example, an appropriate search method may be used to search in theoptimal search interval for the target value of the generator-sideterminal voltage that is able to minimize the generator-side current atpresent. For example, a hill climbing method, a genetic search method,ant a colony search method may be used. An exemplary embodiment of amethod for searching in the optimal search interval for the target valueof the generator-side terminal voltage that is able to minimize thegenerator-side current at present using the hill climbing method will bedescribed below with reference to FIG. 3 .

As another example, the target value of the generator-side terminalvoltage corresponding to a current value of the generator-side currentmay be searched from a pre-established generator-side terminal voltagedata table for the generator, and the searched target value may be usedas the target value of the generator-side terminal voltage that is ableto minimize the generator-side current at present, wherein thegenerator-side terminal voltage data table includes target values of thegenerator-side terminal voltage that are able to minimize thegenerator-side current under different values of the generator-sidecurrent respectively. Further, as an example, the target value of thegenerator-side terminal voltage corresponding to current operatingparameter values (for example, an operating ambient temperature value,and a torque value and a rotational speed value of the generator) andthe current value of the generator-side current may be searched from thepre-established generator-side terminal voltage data table, and thesearched target value may be used as the target value of thegenerator-side terminal voltage that is able to minimize thegenerator-side current at present. Correspondingly, the generator-sideterminal voltage data table may include target values of thegenerator-side terminal voltage that are able to minimize thegenerator-side current under different values of the generator-sidecurrent respectively and under different values of the operating ambienttemperature respectively.

As another example, the target value of the generator-side terminalvoltage corresponding to a current output power value of the generatormay be searched from a pre-established generator-side terminal voltagedata table for the generator, and the searched target value may be usedas the target value of the generator-side terminal voltage that is ableto minimize the generator-side current at present, wherein thegenerator-side terminal voltage data table includes target values of thegenerator-side terminal voltage that are able to minimize thegenerator-side current under different values of the output power valueof the generator respectively.

As an example, the generator-side terminal voltage data table may beobtained through simulation or actual operation for the model of thegenerator.

In step S30, the target value of the generator-side terminal voltage maybe set based on the determined target value upper limit of thegenerator-side terminal voltage and the optimal target value of thegenerator-side terminal voltage.

As an example, under a condition that the determined optimal targetvalue of the generator-side terminal voltage exceeds the determinedtarget value upper limit of the generator-side terminal voltage, thetarget value of the generator-side terminal voltage may be set as thedetermined target value upper limit of the generator-side terminalvoltage; and under a condition that the determined optimal target valueof the generator-side terminal voltage does not exceed the determinedtarget value upper limit of the generator-side terminal voltage, thetarget value of the generator-side terminal voltage may be set as thedetermined optimal target value of the generator-side terminal voltage.

It should be understood that the method for controlling thegenerator-side terminal voltage of the converter according to theexemplary embodiments of the present application may be performedperiodically to achieve dynamic setting of the target value of thegenerator-side terminal voltage.

FIG. 3 illustrates a flowchart of a method for determining an optimaltarget value of a generator-side terminal voltage using a hill climbingmethod according to an exemplary embodiment of the present application.

As shown in FIG. 3 , in step S201, the target value of thegenerator-side terminal voltage may be set to a corresponding initialvalue, and a value I0 of the generator-side current and a given torquevalue T0 of the generator may be obtained after the generator-sideterminal voltage is stable.

Here, the given torque value is a reference torque value.

As an example, under a condition that the method for controlling thegenerator-side terminal voltage of the converter according to theexemplary embodiments of the present application is executed for thefirst time, the initial value may be the minimum value U_(min) in theoptimal search interval; and under a condition that the method forcontrolling the generator-side terminal voltage of the converteraccording to the exemplary embodiments of the present application is notexecuted for the first time, the initial value may be the target valueof the generator-side terminal voltage that is able to minimize thegenerator-side current and is obtained by executing the method forcontrolling the generator-side terminal voltage of the converteraccording to the exemplary embodiments of the present application usingthe hill climbing method last time.

In step S202, the target value of the generator-side terminal voltagemay be set as a sum of the initial value and ΔU, and under a conditionthat the generator-side terminal voltage is stable and the given torquevalue is T0, whether a value I1 of the generator-side current is lessthan I0 may be determined, wherein under a condition that I1 is greaterthan T0, step S203 is performed, and under a condition that I1 is lessthan T0, step S207 is performed. In other words, if increasing thetarget value of the generator-side terminal voltage on the basis of theinitial value can reduce the value of the generator-side current, thetarget value of the generator-side terminal voltage may be increasedcontinually. If increasing the target value of the generator-sideterminal voltage cannot reduce the value of the generator-side current,the target value of the generator-side terminal voltage may be reducedon the basis of the initial value.

Here, ΔU is greater than 0.

It should be understood that after the target value of thegenerator-side terminal voltage is set to the sum of the initial valueand ΔU, I1 is the value of the generator-side current when thegenerator-side terminal voltage is stable and the given torque value isT0.

In step S203, the target value of the generator-side terminal voltagemay be set as a difference between the initial value and ΔU, and under acondition that the generator-side terminal voltage is stable and thegiven torque value is T0, whether a value I2 of the generator-sidecurrent is less than 10 may be determined, wherein under a conditionthat 12 is greater than I0, step S204 is performed, that is, the initialvalue is determined as the target value of the generator-side terminalvoltage that is able to minimize the generator-side current at present;and under a condition that 12 is less than I0, step S205 is performed.

In step S205, it is proceeded to a next setting: the target value of thegenerator-side terminal voltage set last time reduced by ΔU may be usedas the target value of the generator-side terminal voltage set thistime, and under a condition that the generator-side terminal voltage isstable and the given torque value is T0, whether a current value of thegenerator-side current is smaller than a previous value of thegenerator-side current may be determined, wherein under a condition thatthe current value of the generator-side current is greater than theprevious value of the generator-side current, step S206 is performed,that is, the target value of the generator-side terminal voltage setlast time is determined as the target value of the generator-sideterminal voltage that is able to minimize the generator-side current atpresent; and under a condition that the current value of thegenerator-side current is smaller than the previous value of thegenerator-side current, step S205 is repeated.

For example, under a condition that step S205 is performed for the firsttime after step S203, the target value of the generator-side terminalvoltage set last time is the initial value −ΔU, then the target value ofthe generator-side terminal voltage set this time is the initial value−2ΔU; and under a condition that the generator-side terminal voltage isstable and the given torque value is T0, whether the current value ofthe generator-side current is smaller than the previous value of thegenerator-side current (i.e., I2) may be determined. It should beunderstood that when step S205 is repeatedly performed, it is proceededto a next setting, and the target value of the generator-side terminalvoltage set when step S205 was performed last time may be reduced by astep size of ΔU.

In step S207, it is proceeded to a next setting: the target value of thegenerator-side terminal voltage set last time increased by ΔU may beused as the target value of the generator-side terminal voltage set thistime, and under a condition that the generator-side terminal voltage isstable and the given torque value is T0, whether a current value of thegenerator-side current is smaller than a previous value of thegenerator-side current may be determined, wherein under a condition thatthe current value of the generator-side current is greater than theprevious value of the generator-side current, step S208 is performed,that is, the target value of the generator-side terminal voltage setlast time is determined as the target value of the generator-sideterminal voltage that is able to minimize the generator-side current atpresent; and under a condition that the current value of thegenerator-side current is smaller than the previous value of thegenerator-side current, step S207 is repeated;

It should be understood that the search range of the entire searchprocess is limited to the optimal search interval.

As an example, the search equation of the above search process can beexpressed by equation (5):

$\begin{matrix}{U_{{set}1} = {{U_{{set}0} + {{\Delta U}{if}T_{1}}} = {T_{0}\left\{ \begin{matrix}{{{{if}I_{0}} > {I_{1}{do}U_{{set}2}}} = {U_{{set}1} + {{\Delta U}{until}{}I_{N}{is}{the}{minimum}}}} \\{{{{if}I_{0}} < {I_{1}{do}U_{{set}2}}} = {U_{{set}0} - {{\Delta U}{until}{}I_{N}{is}{the}{minimum}}}}\end{matrix} \right.}}} & (5)\end{matrix}$

Wherein U_(set1) is the current target value of the generator-sideterminal voltage, U_(set0) is the last target value of thegenerator-side terminal voltage, T₁ is the current given torque value,T₀ is the last given torque value, I₁ is the current value of thegenerator-side current, T₀ is the last value of the generator-sidecurrent, U_(set2) is the next target value of the generator-sideterminal voltage, and I_(N) is the minimum value of the generator-sidecurrent.

FIG. 4 illustrates a structural block diagram of a controller of aconverter according to an exemplary embodiment of the presentapplication.

As shown in FIG. 4 , the controller of the converter according to theexemplary embodiment of the present application includes a target valueupper limit determination unit 100, an optimum target valuedetermination unit 200, and a target value setting unit 300.

Specifically, the target value upper limit determination unit 100 may beconfigured to determine a target value upper limit of the generator-sideterminal voltage based on a current voltage value of a direct-current(DC) bus of the converter, wherein the generator-side terminal voltageis a terminal voltage of a generator whose output terminal is connectedto the converter.

As an example, the target value upper limit determination unit 100 maybe configured to determine, on the basis of the current voltage value ofthe DC bus of the converter, the target value upper limit of thegenerator-side terminal voltage further based on at least one of apreset maximum availability of a voltage of the DC bus, a voltage losscorresponding to a dead time of an IGBT module in a generator-siderectifier unit of the converter, and an on-state voltage drop of theIGBT module in the generator-side rectifier unit of the converter.

The optimal target value determination unit 200 may be configured todetermine a target value of the generator-side terminal voltage that isable to minimize a generator-side current at present, and use thedetermined target value of the generator-side terminal voltage as anoptimal target value of the generator-side terminal voltage, wherein thegenerator-side current is an output current of the generator.

As an example, the optimal target value determination unit 200 may beconfigured to determine whether a current generator-side terminalvoltage belongs to a preset optimal search interval; and set, under acondition that it is determined that the current generator-side terminalvoltage belongs to the optimal search interval, the target value of thegenerator-side terminal voltage to different values in the optimalsearch interval in sequence, so as to search in the optimal searchinterval for the target value of the generator-side terminal voltagethat is able to minimize the generator-side current at present, whereinunder a condition that the generator-side terminal voltage belongs tothe optimal search interval, the generator-side terminal voltage is in acontrollable state.

As an example, the optimal target value determination unit 200 may beconfigured to perform the followings operations: operation (a): settingthe target value of the generator-side terminal voltage to acorresponding initial value, and obtaining a value I0 of thegenerator-side current and a given torque value T0 of the generatorafter the generator-side terminal voltage is stable; operation (b):setting the target value of the generator-side terminal voltage as a sumof the initial value and ΔU, and under a condition that thegenerator-side terminal voltage is stable and the given torque value isT0, determining whether a value I1 of the generator-side current is lessthan I0, wherein under a condition that I1 is greater than I0, operation(c) is performed, and under a condition that I1 is less than I0,operation (e) is performed; operation (c): setting the target value ofthe generator-side terminal voltage as a difference between the initialvalue and ΔU, and under a condition that the generator-side terminalvoltage is stable and the given torque value is T0, determining whethera value I2 of the generator-side current is less than I0, wherein undera condition that 12 is greater than I0, the initial value is determinedas the target value of the generator-side terminal voltage that is ableto minimize the generator-side current at present, and under a conditionthat 12 is less than I0, operation (d) is performed; operation (d):proceeding to a next setting: using the target value of thegenerator-side terminal voltage set last time reduced by ΔU as thetarget value of the generator-side terminal voltage set this time, andunder a condition that the generator-side terminal voltage is stable andthe given torque value is T0, determining whether a current value of thegenerator-side current is smaller than a previous value of thegenerator-side current, wherein under a condition that the current valueof the generator-side current is greater than the previous value of thegenerator-side current, the target value of the generator-side terminalvoltage set last time is determined as the target value of thegenerator-side terminal voltage that is able to minimize thegenerator-side current at present, and under a condition that thecurrent value of the generator-side current is smaller than the previousvalue of the generator-side current, operation (d) is repeated;operation (e): proceeding to a next setting: using the target value ofthe generator-side terminal voltage set last time increased by ΔU as thetarget value of the generator-side terminal voltage set this time, andunder a condition that the generator-side terminal voltage is stable andthe given torque value is T0, determining whether a current value of thegenerator-side current is smaller than a previous value of thegenerator-side current, wherein under a condition that the current valueof the generator-side current is greater than the previous value of thegenerator-side current, the target value of the generator-side terminalvoltage set last time is determined as the target value of thegenerator-side terminal voltage that is able to minimize thegenerator-side current at present, and under a condition that thecurrent value of the generator-side current is smaller than the previousvalue of the generator-side current, operation (e) is repeated; whereinΔU is greater than 0.

As another example, the optimal target value determination unit 200 maybe configured to search, from a pre-established generator-side terminalvoltage data table for the generator, the target value of thegenerator-side terminal voltage corresponding to a current value of thegenerator-side current or an output power value of the generator, anduse the searched target value as the target value of the generator-sideterminal voltage that is able to minimize the generator-side current atpresent, wherein the generator-side terminal voltage data table includestarget values of the generator-side terminal voltage that are able tominimize the generator-side current under different values of thegenerator-side current respectively, or includes target values of thegenerator-side terminal voltage that are able to minimize thegenerator-side current under different values of the output power valueof the generator respectively.

The target value setting unit 300 may be configured to set the targetvalue of the generator-side terminal voltage based on the determinedtarget value upper limit of the generator-side terminal voltage and theoptimal target value of the generator-side terminal voltage.

As an example, the target value setting unit 300 may be configured toset, under a condition that the determined optimal target value of thegenerator-side terminal voltage exceeds the determined target valueupper limit of the generator-side terminal voltage, the target value ofthe generator-side terminal voltage as the determined target value upperlimit of the generator-side terminal voltage; and set, under a conditionthat the determined optimal target value of the generator-side terminalvoltage does not exceed the determined target value upper limit of thegenerator-side terminal voltage, the target value of the generator-sideterminal voltage as the determined optimal target value of thegenerator-side terminal voltage.

It should be understood that the specific processing performed by thecontroller of the converter according to the exemplary embodiments ofthe present application has been described in detail with reference toFIG. 2 to FIG. 3 , and the relevant details will not be repeated here.

It should be understood that each unit in the controller of theconverter according to the exemplary embodiments of the presentapplication may be implemented as a hardware component and/or a softwarecomponent. Those skilled in the art can implement each unit by using,for example, a Field Programmable Gate Array (FPGA) or an ApplicationSpecific Integrated Circuit (ASIC) according to the defined processingperformed by each unit.

The exemplary embodiments of the present application provide acomputer-readable storage medium having computer programs storedthereon, wherein the computer programs, when executed by a processor,implement the method for controlling the generator-side terminal voltageof the converter described in the above exemplary embodiments. Thecomputer-readable storage medium is any data storage device that canstore data being readable by a computer system. Examples of thecomputer-readable storage media may include a read-only memory, arandom-access memory, an optical disk, a magnetic tape, a floppy disk,an optical data storage device, and a carrier wave (such as datatransmission over the Internet via wired or wireless transmissionpaths).

A controller of a converter according to an exemplary embodiment of thepresent application may include a processor (not shown) and a memory(not shown), wherein the memory has computer programs stored thereon,and the computer programs, when executed by the processor, implement themethod for controlling the generator-side terminal voltage of theconverter as described in the above exemplary embodiments.

While a few exemplary embodiments of the present application have beenshown and described, those skilled in the art will appreciate thatmodifications can be made to these embodiments without departing fromthe principle and spirit of the present application whose scope islimited by the claims and their equivalents.

1. A method for controlling a generator-side terminal voltage of aconverter, the method comprising: determining a target value upper limitof the generator-side terminal voltage based on a current voltage valueof a direct-current (DC) bus of the converter, wherein thegenerator-side terminal voltage is a terminal voltage of a generatorwhose output terminal is connected to the converter; determining atarget value of the generator-side terminal voltage that is able tominimize a generator-side current at present, and using the determinedtarget value of the generator-side terminal voltage as an optimal targetvalue of the generator-side terminal voltage, wherein the generator-sidecurrent is an output current of the generator; and setting the targetvalue of the generator-side terminal voltage based on the determinedtarget value upper limit of the generator-side terminal voltage and theoptimal target value of the generator-side terminal voltage.
 2. Themethod according to claim 1, wherein the step of setting the targetvalue of the generator-side terminal voltage based on the determinedtarget value upper limit of the generator-side terminal voltage and theoptimal target value of the generator-side terminal voltage comprises:setting, under a condition that the determined optimal target value ofthe generator-side terminal voltage exceeds the determined target valueupper limit of the generator-side terminal voltage, the target value ofthe generator-side terminal voltage as the determined target value upperlimit of the generator-side terminal voltage; and setting, under acondition that the determined optimal target value of the generator-sideterminal voltage does not exceed the determined target value upper limitof the generator-side terminal voltage, the target value of thegenerator-side terminal voltage as the determined optimal target valueof the generator-side terminal voltage.
 3. The method according to claim1, wherein the step of determining the target value of thegenerator-side terminal voltage that is able to minimize thegenerator-side current at present comprises: determining whether acurrent generator-side terminal voltage belongs to a preset optimalsearch interval; and setting, under a condition that it is determinedthat the current generator-side terminal voltage belongs to the optimalsearch interval, the target value of the generator-side terminal voltageto different values in the optimal search interval in sequence, so as tosearch in the optimal search interval for the target value of thegenerator-side terminal voltage that is able to minimize thegenerator-side current at present, wherein under a condition that thegenerator-side terminal voltage belongs to the optimal search interval,the generator-side terminal voltage is in a controllable state.
 4. Themethod according to claim 1, wherein the step of determining the targetvalue upper limit of the generator-side terminal voltage based on thecurrent voltage value of the DC bus of the converter comprises:determining, on the basis of the current voltage value of the DC bus ofthe converter, the target value upper limit of the generator-sideterminal voltage further based on at least one of: a preset maximumavailability of a voltage of the DC bus, a voltage loss corresponding toa dead time of an IGBT module in a generator-side rectifier unit of theconverter, and an on-state voltage drop of the IGBT module in thegenerator-side rectifier unit of the converter.
 5. The method accordingto claim 3, wherein the step of setting the target value of thegenerator-side terminal voltage to different values in the optimalsearch interval in sequence, so as to search in the optimal searchinterval for the target value of the generator-side terminal voltagethat is able to minimize the generator-side current at presentcomprises: step (a): setting the target value of the generator-sideterminal voltage to a corresponding initial value, and obtaining a valueI0 of the generator-side current and a given torque value T0 of thegenerator after the generator-side terminal voltage is stable; step (b):setting the target value of the generator-side terminal voltage as a sumof the initial value and ΔU, and under a condition that thegenerator-side terminal voltage is stable and the given torque value isT0, determining whether a value I1 of the generator-side current is lessthan T0, wherein under a condition that I1 is greater than T0, step (c)is performed, and under a condition that I1 is less than T0, step (e) isperformed; step (c): setting the target value of the generator-sideterminal voltage as a difference between the initial value and ΔU, andunder a condition that the generator-side terminal voltage is stable andthe given torque value is T0, determining whether a value I2 of thegenerator-side current is less than T0, wherein under a condition that12 is greater than T0, the initial value is determined as the targetvalue of the generator-side terminal voltage that is able to minimizethe generator-side current at present, and under a condition that 12 isless than T0, step (d) is performed; step (d): proceeding to a nextsetting: using the target value of the generator-side terminal voltageset last time reduced by ΔU as the target value of the generator-sideterminal voltage set this time, and under a condition that thegenerator-side terminal voltage is stable and the given torque value isT0, determining whether a current value of the generator-side current issmaller than a previous value of the generator-side current, whereinunder a condition that the current value of the generator-side currentis greater than the previous value of the generator-side current, thetarget value of the generator-side terminal voltage set last time isdetermined as the target value of the generator-side terminal voltagethat is able to minimize the generator-side current at present, andunder a condition that the current value of the generator-side currentis smaller than the previous value of the generator-side current, step(d) is repeated; and step (e): proceeding to a next setting: using thetarget value of the generator-side terminal voltage set last timeincreased by ΔU as the target value of the generator-side terminalvoltage set this time, and under a condition that the generator-sideterminal voltage is stable and the given torque value is T0, determiningwhether a current value of the generator-side current is smaller than aprevious value of the generator-side current, wherein under a conditionthat the current value of the generator-side current is greater than theprevious value of the generator-side current, the target value of thegenerator-side terminal voltage set last time is determined as thetarget value of the generator-side terminal voltage that is able tominimize the generator-side current at present, and under a conditionthat the current value of the generator-side current is smaller than theprevious value of the generator-side current, step (e) is repeated;wherein ΔU is greater than
 0. 6. The method according to claim 1,wherein the step of determining the target value of the generator-sideterminal voltage that is able to minimize the generator-side current atpresent comprises: searching, from a pre-established generator-sideterminal voltage data table for the generator, the target value of thegenerator-side terminal voltage corresponding to a current value of thegenerator-side current or an output power value of the generator, andusing the searched target value as the target value of thegenerator-side terminal voltage that is able to minimize thegenerator-side current at present, wherein the generator-side terminalvoltage data table comprises target values of the generator-sideterminal voltage that are able to minimize the generator-side currentunder different values of the generator-side current respectively, orcomprises target values of the generator-side terminal voltage that areable to minimize the generator-side current under different values ofthe output power value of the generator respectively.
 7. A device forcontrolling a generator-side terminal voltage of a converter, the devicecomprising: a target value upper limit determination unit configured todetermine a target value upper limit of the generator-side terminalvoltage based on a current voltage value of a direct-current (DC) bus ofthe converter, wherein the generator-side terminal voltage is a terminalvoltage of a generator whose output terminal is connected to theconverter; an optimal target value determination unit configured todetermine a target value of the generator-side terminal voltage that isable to minimize a generator-side current at present, and using thedetermined target value of the generator-side terminal voltage as anoptimal target value of the generator-side terminal voltage, wherein thegenerator-side current is an output current of the generator; and atarget value setting unit configured to set the target value of thegenerator-side terminal voltage based on the determined target valueupper limit of the generator-side terminal voltage and the optimaltarget value of the generator-side terminal voltage.
 8. The deviceaccording to claim 7, wherein the target value setting unit isconfigured to set, under a condition that the determined optimal targetvalue of the generator-side terminal voltage exceeds the determinedtarget value upper limit of the generator-side terminal voltage, thetarget value of the generator-side terminal voltage as the determinedtarget value upper limit of the generator-side terminal voltage; andset, under a condition that the determined optimal target value of thegenerator-side terminal voltage does not exceed the determined targetvalue upper limit of the generator-side terminal voltage, the targetvalue of the generator-side terminal voltage as the determined optimaltarget value of the generator-side terminal voltage.
 9. The controlleraccording to claim 7, wherein the optimal target value determinationunit is configured to determine whether a current generator-sideterminal voltage belongs to a preset optimal search interval; and set,under a condition that it is determined that the current generator-sideterminal voltage belongs to the optimal search interval, the targetvalue of the generator-side terminal voltage to different values in theoptimal search interval in sequence, so as to search in the optimalsearch interval for the target value of the generator-side terminalvoltage that is able to minimize the generator-side current at present,wherein under a condition that the generator-side terminal voltagebelongs to the optimal search interval, the generator-side terminalvoltage is in a controllable state.
 10. The device according to claim 7,wherein the target value upper limit determination unit is configured todetermine, on the basis of the current voltage value of the DC bus ofthe converter, the target value upper limit of the generator-sideterminal voltage further based on at least one of: a preset maximumavailability of a voltage of the DC bus, a voltage loss corresponding toa dead time of an IGBT module in a generator-side rectifier unit of theconverter, and an on-state voltage drop of the IGBT module in thegenerator-side rectifier unit of the converter.
 11. The device accordingto claim 7, wherein the device is arranged in a controller of aconverter.
 12. A controller of a converter, wherein the controllercomprises: a processor; a memory having computer programs storedthereon, wherein the computer programs, when executed by the processor,implement the method for controlling the generator-side terminal voltageof the converter according to claim
 1. 13. A computer-readable storagemedium having computer programs stored thereon, wherein the computerprograms, when executed by a processor, implement the method forcontrolling the generator-side terminal voltage of the converteraccording to claim 1.